Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 erent in ff Chemistry and Physics Discussions Atmospheric , and K. L. Leong 2 , L. L. Song 1 4808 4807 , B. M. Wang 1 , X. Y. Luo 1 ect the air quality of PRD. Under the subsidence, the wind ff , W. Yu 1 ected by the local circulation and the features of ABL are di ff , Q. Fan 1 erent kinds of ABL characteristics in PRD: when the surface winds in PRD were ff and Physics (ACP). Please refer to the corresponding final paper in ACP if available. This discussion paper is/has been under review for the journal Atmospheric Chemistry Department of Atmospheric Sciences, SunClimate yat-sen Center University, Guangzhou, of 510275, Guangdong China Province,Macao Guangzhou, Meteorological 510080, and China Geophysical Bureau, Macao, China at Xinken station and the mountain-valley circulation at Qingyuan station. When the are obvious, but theis diurnal obviously variation a ofvarious ABL stations. on rainy A days simulationdays from is focus 12–15 not on July obvious. 2006, high occurreda pollution tropical under The episode cyclone high ABL “Bilis”. pressure during conditions, Comparing thestructure accompanied the subsidence by simulated with vertical the wind ABL fieldsfound and measurements temperature that, at the Xinken, Panyu modelleddi and and Qingyuan measured station, atmospheric itlight fields was or reveal almost that calm, the there local are circulation two was dominated, such as the sea-land breeze simulations by the WRF mesoscaletics model in PRD. were From used three to kindsdays analyse of and the weather sunny condition ABL simulations characteris- days)wind (subsidence by days, fields rainy WRF in model, theseThe three it results cases was show were that found the moderately that diurnal consistent the variation with of simulated the ABL temperature, measurements. in subsidence days and sunny days found that in summer, thethere surface usually winds in is PRD vertical areten wind more influenced shear controlled by at by the the the tropicala south, height cyclone/typhoon. and tropical of The 800 cyclone subsidence m and willspeed or precipitation in a so, from therefore, ABL PRD andtions. is the When of- height the of background wind ABLXinken speed will is change small decrease dramatically or and with calm, height, resulttions, the such which wind in as profile is high the at perhaps sea level Panyu caused and land concentra- breeze. by For the more local understanding circula- about the ABL of PRD, the Atmospheric conditions areepisodes often especially in connected urbanpaign, with atmospheric areas. boundary the layer As (ABL) occurrence measurementsPanyu part were and of carried of Xinken out in at high the the Qingyuan, PRIDE-PRD2006 Pearl pollution River intensive Delta cam- (PRD) from 1 July to 30 July of 2006. It was 1 2 3 Received: 6 July 2010 – Accepted: 16Correspondence December to: 2010 Q. Fan – ([email protected]) Published: 9Published February by 2011 Copernicus Publications on behalf of the European Geosciences Union. Abstract Atmospheric boundary layer characteristics over the Pearl RiverChina Delta, during summer 2006: measurement and model results S. J. Fan Atmos. Chem. Phys. Discuss., 11,www.atmos-chem-phys-discuss.net/11/4807/2011/ 4807–4842, 2011 doi:10.5194/acpd-11-4807-2011 © Author(s) 2011. CC Attribution 3.0 License. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; Ska- http://www.wrf-model.org/index.php 4810 4809 The vertical structure, as well as the spatial and temporal variability of the ABL, is The ABL measurements were a very important part of these two intensive cam- tropical cyclone or sea-land breeze. Their studies (Feng et al., 2007; Wu et al., 2005) strated that manyMM5 meteorological or characteristics WRF in mesoscaleFurthermore, the models accurate ABL (Kwun depiction can etimportant of al., be meteorological for 2009; represented conditions air Zhu, by withinmixing pollution 2008; layer the height, Miao modelling. the ABL et turbulent is kineticculation al., Knowledge energy are also 2009). (TKE) of all and essential, the the especially horizontalet temperature, in or al., vertical cases the 2009; cir- of wind, server Hannasome air model et the pollution studies al., episodes (Feng 2010; et (Prtenjak air al., Gilliam pollution 2007; et episodes Wu in et al., al., PRD 2010; 2005) region also Hu are showed very et that often al., most associated severe 2010). with the Results subsidence from by For this purpose, we applied themarock WRF et (WRF, al., 2007) modelthis that simulates paper. atmospheric circulation at a regional scale in very important in numerical weather prediction (NWP). Many researches have demon- motion outside of Typhoontions. and sea The breeze presencethe would of formation result of anti-cyclone in three high-pressure inversion thevertical systems layers profiles high-level and and of concentra- two the sea aerosolobservations wind layers breeze from velocity as lead 3 over well stations Xinken to as only. station.not quite Limited present specific This to the study the detailed was resolution horizontalCompared based of and to on the vertical the the observations, characteristics it investigation ofments, can- of ABL a Fan in et numerical PRD al. regions. simulation (2008), of besides the the local analysis circulation of in measure- PRD region was conducted. essential to the air quality problem. paigns. The characteristicsPRD of in October ABL 2004 observations werevational analysed at in results Qingyuan, a showed previous Panyu study that and (Fan a et Xinken al., surface in 2008). high-pressure The system obser- (anti-cyclone), descent 2008b). The characteristics of the wind, humidity and thermodynamic conditions are reaction process and physical optical characteristicsXiao (Liu et et al., al., 2008; 2009; Jung Lu et et al., 2009; al., 2010; Zhang et al., 2008; Rose et al., 2010; Cheng et al., development and urban expansion.changed. The In land orderrecently, use to “Programme of and reveal Regional the land Integrated meteorologicalRiver cover Experiments and Delta” of have Air (PRIDE-PRD) dramatically chemical Quality campaign characteristics overof 2004 the in researches Pearl and PRD focused on 2006 these2008; were experimental Li conducted results et and (Hua al., a etal., 2010; al., number 2009; Lou 2008; Zhang et et Garland al., al, etmeteorological 2010; 2008a,b; al., Cheng fields Yu et et were al., al., closely 2008a). 2010; interacting Many with Verma results et the pointed chemical al., out composition, 2009; that chemical the Miyazaki et including the city ofZhongshan Guangzhou, and Shenzhen, Zhuhai, Foshan, sometimes Dongguan, includingseveral Hongkong Huizhou, investigations and on Jiangmen, Macao. the There characteristics havePRD of been from atmospheric boundary the layer 1980s (ABL)But to over in 1990s the (Huang last and two Liu, decades, 1985; PRD Guo, region 1991; has Liang experienced et a al., period 1992). of rapid economic 1 Introduction The Pearl River Delta (PRD),China, one China of is the situated thirdtrial in largest area the Gross situated middle Domestic in Product of aal., in Guangdong region 2004; China. province, of Liu It very et is complex al., wind aSea, 2002). regimes coastal, in The (Chen indus- the south et of north al., Guangdong isarea province 2009; the is Ding with Nan facing et more the Ling South Mountain than China and 100 in the million centre people is (Fig. PRD, a 1a rapidly and growing b). PRD contains many cities, tem and the wind directionsalso were suggest almost that the the same. highby Air Furthermore, subsidence. Pollutant the index modelled (API) results episode was caused predominately surface winds were strong, the stations were under the same background weather sys- 5 5 25 15 20 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N, N, ◦ ◦ E). ◦ N, 113.26 ◦ resolution. A lot of researches pointed out 2 4812 4811 1 km × E), about 50 km north from the Central Guangzhou. Guangzhou E), about 20 km south from Central Guangzhou, in the middle of er a detailed insight in the fine-scale lower-tropospheric conditions, ◦ ◦ ff E), in the northE), of in PRD. Xinken the station south was of located in PRD. Xinken Qingyuan town and (22.37 Xinken represent a more rural envi- N, 113.07 N, 113.19 ◦ ◦ ◦ ◦ Guangzhou back garden and Guangzhou station conducted an automatic weather In this study, we investigate the detailed characteristics of ABL in summer 2006 in at Guangzhou station duringweather July from 2006. 12–14 There were July two and periods 23–25 of July, high temperature corresponding to strong tropical cyclone (23.55 station was located onronmental the Monitoring 16th Center floor (GPEMC) building (50 m (23.13 a.g.l.) of2.2 the Guangdong Provincial Weather conditions Envi- in July 2006 According to the Centralical Meteorological Station conditions of over Guangdong PRDmuch province, precipitation. in meteorolog- July Figure 2 2006 shows were the characterised measured temperature, by precipitation high and temperature API and and direction were given between 0mean and temperature 2000 was m reported with a with vertical a resolution vertical of resolution 50 m, of while station 10 m. by obtaining hourly windtive speed, humidity. wind Guangzhou direction, back temperature, garden radiation station and was rela- located in Guangzhou back garden ronment. At Qingyuan station,radar. vertical measurements Mean were wind made speedmatically with derived and meteorological from direction, radio soundings. temperature Theseper and parametres day relative between were 0 reported humidity and several were times 3000stations, m auto- with radio a soundings vertical were resolutiontemperature. of performed 100 Radio to m. soundings obtain At were Panyu launched mean and seven18:00, Xinken velocity, times 20:00, wind (06:00, 08:00, 23:00 direction LST) 10:00, and 14:00, or08:00, eleven 10:00, 14:00, times 17:00, (intensive 18:00, observation, 19:00, 02:00, 20:00, 23:00 06:00, LST) 07:00, per day. Mean wind speed sounding observation.(22.56 Panyu station wasPRD. located Qingyuan at station Panyu113.03 meteorological was Bureau located in113.35 Qingyuan meteorological bureau (23.40 Panyu and Xinken. In these stations, Qingyuan, Panyu and Xinken conducted the In order to studywere selected, the as characteristics shown of in Fig. ABL 1b, over Qingyuan, PRD Guangzhou area, back garden, five Guangzhou, observational sites 2 Experimental set up and synoptic2.1 situations Experimental set up The selected PRD intensive campaign periodlower was pressure in summer. synoptic In systems thispollution period dominate of episodes the and year, by theWu the PRD et region Typhoon’s al., strong usually 2005). experiences descending The motion campaign (Feng began et on 1 al., July 2007; 2006 and ended on 30 July 2006. Besides various horizontal and verticalalso meteorological analysed. fields, the In localdescribed. circulations Sect. The are 2, model settings the andnumerical field simulations model are results experimental involved obtained in set from Sect. 3. the up three-dimensional Conclusions and will synoptic follow in situations the last are Sect. 4. that the high resolutiondevelopment (Mayer forecast et al., was 2010; a Jury key et al., task 2009; for NolanPRD et further region. al., We progress 2009a,b). especially in focusprocess on NWP which three occurred model kinds on of 12–15 weather, Julypollution one 2006, episode. is resulting The in the second a tropical period high cyclone the air is sunny pollution the days index rainy from (API) days 20–23 fromABL July. 14–18 in WRF these July model three and was periods. the utilized The third to simulation is investigate results the are features compared of with the observations. sphere, weak surface winds andon a simulations relatively low provided ABL. byThus, However, their MM5 it study did or was not based WRFwhich o model we at have succeeded awe in horizontal utilized doing resolution WRF in model of this results 12 study. km. at Another 1 novelty of this study is that also pointed out the Typhoon caused a strong descending motion in the lower tropo- 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 223 and × 148, 322 E. Two-way nesting × ◦ ected by the Tropical cy- ff 91, 181 × N and 113 ◦ 4814 4813 C in these three days. Figure 3 shows the surface weather ◦ -resolution global terrain and land use files. The original USGS 00 277 points and a resolution of 27, 9, 3, 1 km, respectively. The central latitude × The main physics options included Lin et al. microphysics; the Betts-Miller-Janjic Influenced by subtropical high pressure and subsidence by strong tropical cyclone scheme was used. cal. Twenty layers wereextracted below from a the height 30 of24-category 2 land km. cover data The was most employed. fine topography inputcumulus was parameterization; the RRTM longwavewave radiation radiation scheme; scheme the and Goddard MRF(D03 short- boundary and layer D04), scheme. itthe was For explicit the assumed microphysical two that parameterization inner the scheme domains convection and was no reasonably cumulus well parameterization resolved by River Estuary, are configured with a367 horizontal grid of 139 and longitude of thewere applied coarse for domain the domains. (D01)processes, For were from the the model 23 to top adequately to resolve the the boundary surface layer level, there were 35 sigma levels in the verti- 3.1 WRF model and settings To study the event, WRF mesoscalefully model compressible was nonhydrostatic employed. equations The on WRF a modelcoordinate staggered consists is Arakawa of C a grid. terrain-following Its hydrostaticorder vertical pressure time coordinate. integration The scheme Runge-Kutta and 3rd tion and 5th the order 3rd advection order schemesgravity-wave in modes vertical in is ones a are utilized. horizontal used. In direc- A this time-split study, small four step domains for (Fig. acoustic 4), and all centred at Pearl on 13 July and12:00 then LST on tracked 14 northwest. July. PRD It region was then west landed or at southwest of Xiapu Bilis in3 during Fujian its province movement. at Model results tropical storm at 14:00 LST on 11 July. It made landfall at Yilan in Taiwan at midnight 2006 over the Western North Pacific. It intensified from a tropical storm to a severe al., 2005) have already pointedhigh out that pollution the weather strong in descendingthe motion PRD. subsidence can The motion result from two in tropicalcharacteristics the API cyclones. in peaks PRD So in from we 12–15were this will illustrated July, especially July the in focus detail were the on synoptic following. also the situation ABL caused during by this period “Bilis”, it appeared as hightemperature exceeded temperature 32 in PRD regionsituation from during 12–15 12–14 July. July, Bilis the originally maximum formed from a tropical depression on 9 July and the sea-land breeze.subsidence. So The in wind this profile study,As we at shown will Panyu discuss in these Fig. station three 2, iscorresponds kinds period very to of I ABL complex the belongs features with rainy to in20–22 the the days PRD. July. subsidence from days As 15–18 from stated July 12–15 in and July, the period period II introduction, III many is researches the (Feng et sunny al., days 2007; from Wu et vertical wind shear atobvious the in height the of south 800clone of m in PRD, or summer. besides, so. The this subsidencethe The region and air influence is precipitation quality of often from in a a sea-landunder tropical PRD. breeze subsidence, cyclone The is which are wind will vital speed resultsounding to data in in in the the this air ABL experiment pollutionor and show episode. calm, the that the The when ABL wind analysis the heightwhich fields from background will is at the wind decrease perhaps Panyu speed and caused is Xinken small by station the change local dramatically circulations, with such height, as the heat island circulation fluenced by these two tropicaloccurred cyclone in processes. 15–17 July Two strongwere and precipitation more 26–30 processes dominated July. by the Inthe subtropical other surface high sunny winds pressure. days, in It the PRDveer was are whole to found more PRD that north controlled in regions from by July midnight the 2006, to south, and morning the in winds the sometimes north areas in PRD. There was usually “Bilis” and typhoon “Kaemi”, respectively. There were also two peaks in API values in- 5 5 20 25 15 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cients ffi 2 C and 1.5% in

◦ / ) o j,k o j,k C C − + m j,k

m j,k C

C o j,k ( C 1 = N − k X 1 m j,k = M j X C

1.08, 1.80, and 2.19 1 1 − = N MN cients are all about 0.4 and the values k X 1 ffi = = M j X is the number of numerical hours excluding FAE 1 4816 4815 N MN 2 = grid data. In this study, 12 h were used for the / 1 C and 1.2% in period III, indicating a good overall ◦ ◦ # 1 2 represent the modelled and the observed values, re- × ) ◦ o o j,k C erent ABL features, three kinds of weather were chosen. C ff ) MAGE − and o j,k m j,k C m C ( − C 1 erences in the angle between modelled directions and observed = ff N m j,k k X C 1 ( N 1 " = N 1.26, 1.31, and 1.63 1 cient reaching 0.72 and 0.91, respectively. The values of MB, MAGE, k X − = M 1 ffi j X = M j X is the number of stations and 1 M 1 M = MN = ), mean bias (MB), mean absolute gross error (MAGE), root mean squared error The time series of the hourly 2-m temperature, 10-m wind speed and wind direction In order to represent the di R in 15 July. Inwith the the case observations of in wind terms speed, of WRF diurnal simulations variations were and in magnitudes moderate during agreement most time. finding the actual di directions. In all, thedays simulated (period results III) in are the better than subsidence those days in (period the I)observed rainy and days at in (period Guangzhou sunny II). stationsimulations, from are 12 shown to inwell 15 Fig. July in 5. (period the I), ItThe simulations and can increase of the be of temperature the corresponding seen duringmodel that diurnal 14 tended the July variation to model was under tendency captured performed predict well of generally the by air temperature WRF especially model, surface from but temperature. the 12 July to 13 July and agreement between the observationsdirections and in the three simulations. periods, theof For correlation MB, wind coe MAGE, speed RMSE, andmost and wind of FAE the indicated time. thewind It model directions, should overestimated be MB, the mentioned MAGE, wind that RMSE, fields because and in of FAE the for vector wind characteristics directions of were calculated by RMSE spectively. From the definitions above, thezero, MB, the MAGE, model RMSE, simulations and best. FAEspeed are It in more should period near be II, noted thein in three average Table 1 periods simulated that are wind except all direction,the for close wind the simulated to speed wind temperature the and and observations. the temperature Thererelation observations are in coe good period correlations between I andRMSE, period and FAE III, with with respect theperiod to cor- temperature I are and Where the spinning up time, domain 4 (shown into Fig. evaluate the 4). performance of Table model( 1 simulations, show including some the correlation commonly(RMSE), coe statistical and variables fractional absolute used erroras (FAE). follows MB, (Yu MAGE, et RMSE, al., and 2005): FAE are defined MB characteristics of ABL in PRD. 3.2.1 Measured vs. modelled data In order to validate thethe WRF available simulation results, surface the observations model results furnished were by compared with the main meteorological stations in simulations, the lateral andNCEP/NCAR initial reanalysis conditions for daily WRF 1 spinning simulations up were time. obtained from 3.2 Model results For more understandingA about WRF the mesoscale summer model boundary was layer employed characteristics to of study PRD, the detail horizontal and vertical The first simulation period15 (period July I) was 2006, fromriod corresponding 00:00 II) UTC to began 12 at the Julyperiod 00:00 2006 subsidence UTC represented to 14 days. the 00:00 July UTC rainy20 2006 The July days. and 2006 ended second to The at 00:00 simulation UTC third 00:00 23 UTC (pe- simulation July 18 2006, period July corresponding was 2006, to the from this sunny 00:00 days. UTC In all these 5 5 20 25 15 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent usion ff ff 4818 4817 ected by the local circulation, such as sea-land breeze. ff usion process. The variation of the modelled WRF ABL height for ff Figure 7 shows measured air pollutant concentrations at Guangzhou station from The simulated ABL heights during the night of subsidence days were much lower The daily evolutions and magnitude of ABL height at Xinken station were all di In all the five stations, the simulated diurnal variation of ABL height in subsidence height was high, the air concentrations were comparatively low under the good di the daytime were moderately consistenttime with were the much lidar lower results,heights than but were the the near heights measurements. zero. in Itlayer In night- was parameterization some caused scheme by stations, used the the in MRFscheme the simulated high in model. ABL resolution the planetary nighttime The were boundary ABL much heights lower. calculated by this 13 July to 22concentrations, July. it Comparing can the be simulatedrelated seen ABL to that height the the results meteorological conditions temporal with closely. variations the From of observed 13 July air air to concentrations 14 were July, when the ABL than those in other days.ABL Influenced height by will the be descentmaximum motion, ABL decreased. height the in ABL The the isthe daytime observations stable reached night and from 1500 the of m lidar or subsidencecapture signals so, the days and showed diurnal the dropped that variation ABL to tendency height the of during several ABL hundred height metres. and the simulated WRF ABL model heights in can ABL height at Xinkena from very 09:00 LST low onpollution value. 13 episode. July From to The the 07:00 wind ABL LSTwind profile on was speed measurements, the 14 changed of vertical July dramatically static windthe maintained in direction stability, ABL these and which height two at was daysfields Xinken at beneficial at to Xinken. Xinken to have were the It beenthe complex could high system lower because wind, have than it it caused those locates is in in also a the other Pearl stations. River Estuary. The wind Besides Whereas in theseveral nighttime, hundred the metres. Compared ABL withABL are these height four most at stations, Xinken stable, the are dailymaximum with very evolutions of of the special. ABL the For heights height example,lower all at in than the Xinken lower those subsidence was in than days, around other the stations. 400 daily m The at occurrence 08:00 time LST, was which also was earlier. much Besides, the 2–3 h after the sunrise, reaching up to the maximum (1500 m) at about 14:00 LST. of ABL heightcan at be Xinken seen that stations the were development of also a not well-mixed layer clear. begins 08:00–09:00 LST, e.g., In the other four stations, it has strong heating frombackscattering below. signal It observed also at cansurements be YuenLong are from station seen Hongkong in from University ofby the Hongkong. science lidar lidar and also These normalized technology. showed The relative lidar observations dence that mea- days there and were sunny obvious days. diurnal In changes the rainy of days, ABL thefrom height diurnal the in variation subsi- was other not fourstation apparent. stations. were much The lower ABL than heights those in in three the simulation periods other at stations Xinken and the diurnal variations YuenLong station in Hongkong are shown in Fig. 6. days and sunny daysthe were change all of ABL more height obviousregime was than instantaneous, to the those the ABL in changed convectionwere quickly rainy regime. of from days. the a stable But nocturnal In in regime rainy subsidence in days, the days nighttime and and sunny a days, free the convection ABL regime when there 3.2.2 Atmospheric boundary layer heights The ABL height isof a boundary critical layer parameterthe information for pollutant on vertical di a dispersion.Qingyuan, finer Back Accurate scale garden, assessment Guangzhou, should Panyusimulation and improve Xinken periods the stations and (Fig. ability the 1b) lidar during to normalized three assess relative backscattering signal observed at 13 July and slightlythe higher observed and after simulated the windsWRF night were model all achieved of good from 14 results the except westwind July. at during direction noon Regarding the of was simulation 13 the northwest, July. period. that At wind but that time, directions, the time, the the wind simulated observed direction result results was were from satisfied. the east. Except for Compared with the measurements, the simulated wind speeds were a little lower during 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent ff 4820 4819 C. At 07:00 LST on 21 July, the model results were consistent with ◦ Figure 9 shows the measured vertical temperature distribution by radar sounding The vertical wind profile measured at Panyu station and the simulated results by than the measurements. and the modelledWRF results model at can Qingyuan capture theespecially station decreasing below on of 1000 m. temperature 14 withperature From July the about 1000 height and 1–2 m at to 21 three 3000the times, July. m, measurements. the At 17:00 On model LST overestimated and 14the 19:00 the measurement LST July, tem- well on below 21 July, 1000 the m,measurements. model but also above reproduced 1000 During m the theseQingyuan model two station. underestimated the periods, It therecreased can with was the also a height be at little about seen inversion 1500 m, in at but the the 1500 m actual model temperature at results values were that lower the temperature in- direction higher than 1000 m hadprofiles changed to reproduced the by east WRF at 23:00the model LST. In wind were general, profiles satisfied. the at wind Panyu Inchanged station subsidence were very day all fast, and very which complex. was sunny mainly The day, wind caused speed by and the direction local circulation. On the morning of 21directions July, above the 1000 wind m directions were changed14:00 LST, mainly dramatically the with southeasterly wind height. and in Wind belowwind all veered 1000 m to the the southwest. ABLs southeast.explored At was The by almost model the results from measurements. in thewas Fig. At south. southwesterly 8d the can and After reproduce beginning the the 16:00the of wind LST, features 21 the southwest changed July, to wind the southeast veeredoccurred wind after at to in 16:00 noon LST. the the At of low south 06:00 21 ABL LST, with July. the The wind height. speed increased The after minimum 16:00 LST wind and speed the wind increased from 00:00 LSTThe in maxima 14 speed located July at andmost several northwest hundred reached which metres the corresponded high. with maximum The thespeed wind at measurements. began direction about After to was 10:00 07:00 al- decrease LST, LST. the andincreased wind maintained again and for veered about to 7 h. the southwest. At In 17:00 LST, Fig. the 8c, wind the speed wind profile was complex. the ABL features can be illustrated by model results more clearly. The wind speed results in Fig. 8b canface. capture the The ABL temporal characteristics resolution quite of well WRF except for model the is near higher sur- than that in the measurements, cancelled on the rainyday day, were so used to the compare. measurementsin It the on can vertical be the wind seen fields subsidence that duringthe there day the ABL subsidence have and at day been and Panyu sunny obvious the station discrepancies low sunny was day. jet from The the at wind under west about allsurface 500 day and m on veered height 14 to at July thevery and 06:00 west low. LST. there at The had The a wind been modelled very16:00 the is ABL LST low height from and height. in the 17:00 LST, the The southwest the WRF ABL wind near model height in the was at all also that the very time ABLs low was changed in to Fig. southwest. 6. The At model regions. Due tomonth were various inadequate. reasons, According toperiods, the the the actual sounding vertical corrected wind data data profileQingyuan in at at station our Panyu these station on three and 14 simulation three the July vertical stations and temperature 21 profile in July at were this analysedWRF in model the on following. 14 July and 21 July are shown in Fig. 8. The sounding measures were concentrations appeared as obvious diurnaland variations the ABL again. height When is the low, ABL this results is in stable 3.2.3 high air concentrations. Vertical wind and temperature distributionThe features vertical radio sounding measure experimentsstations were conducted during at July Panyu and in Xinken 2006.teorological Besides, radar the at vertical Qingyuan measurements station were in made order with to me- explore the ABL features in di a subtropical high pressureof the system low and ABL akeep height, the tropical the pollutants cyclone strong in “Bilis”. descentperiod the II motion ABL from and 15 The and July the leading combination todeposition weak 17 to by July, surface the comparatively precipitation air wind high process. concentrations acts API had In all to values. the decreased due During sunny to days the from wet 21 July to 22 July, the air condition, and vice verse. During this episode, PRD area was under the influence of 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N) were ◦ . The winds at 1 − ected by the sea-land N) was also south, but ff ◦ erent wind fields can be ff E at 03:00 LST on 13 July ◦ erent from the other three stations. At ff 4822 4821 usion of air pollutants. The detailed simulated horizontal ff . Under the small background system wind fields, the local circulation 1 − erent stations. It can be seen from Fig. 10a that at Xinken station, located in ff erent local circulations dominated PRD regions, and the wind vectors were various Figure 10a and b show the observed and simulated 10-m wind vectors in PRD re- ff the urban regions were underABL the layer. control The of wind divergence, and direction resulted in in Qingyuan stable station and (about low 23.4 Figure 11a shows the coastaldominated areas by (such as the Pearl south.sea River breeze. Estuary, The about The 22.2 air surface converged layerveered and was toward ascended in under the the the north coastaltion. influence region. at The of The 900 wind hPa. wind the fields direction wereGuangzhou There incoming influenced station. was by an the The urban obvious heatcend heat sea-land island island motion breeze circulation and circulation at circula- descend was Panyunorth motion comparatively and were complex. wind weak, fields The the (850 as- horizontal hPa south or (near so) surface) were and apparent. Compared with the coastal areas, and 03:00 LST on 14on July the are local presented circulation. in Fig.noted At 11. 03:00 near LST Here, the on the coast 13 analysisthe July compared is system (Fig. to concentrated 11a) wind adjacent di speed urbanIn cities. is this small, episode, As the the mentionedinfluence local tropical above, from cyclone when circulation “Bilis” “Bilis” is was made essential not landfall to very at various midnight apparent stations. on in 13 PRD July. region The at 03:00 LST on 13 July. various stations in PRD tendThe to winds be in similar Fig. underwas 10d such southwest, were background because almost system it northwest. wind locatesinfluenced fields. The in by wind the the downstream direction south flow in of from Nanling Qingyuan the Mountain station slopes areas, of3.2.5 which the was high mountains. Vertical circulation from 12 JulyModelled to vertical 14 cross-sections July of wind vectors along 113.2 wind vectors in PRDferent region from at Fig. 08:00 10a LSTFig. 10c, on and the 14 b, aforementioned stations July the wereical and wind all cyclone controlled 14:00 fields “Bilis” LST by had at west. on already“Bilis”. At various 14 made that The stations time, July. landfall, average the wind seem PRD trop- Dif- speed regions very at were Guangzhou similar. deeply in influenced 14 In July by was 3.46 m s is essential to various stations. Figure 10c and d shows the observed and simulated was 1.54 m s other stations. At 00:00 LSTthose on at 13 20:00 LST July on (Fig.The 12 10b), winds July the (Fig. at wind 10a), Xinken speeds the stationbreeze. were local changed At smaller circulations Panyu to than were and the also Guangzhou west,but stations, very the it the obvious. wind wind was directions speeds also were decreased. a stillto At from the the Guangzhou east west, back and gardentions station, at were the Qingyuan influenced winds station by veered the thethat local winds time, circulation, changed the di to tropical southeast.“Bilis” cyclone and “Bilis” These still PRD two had sta- region not was made far. landfall, the The distance average between wind speed at Guangzhou on 12 July wind direction was southeastin and the the urban wind centre, the speedGuangzhou wind decreased. veered back toward garden At the station, Guangzhou easttion, and the station, the the wind wind wind speed changed speed to decreased increased.the south. again. observations. At The The simulated At wind wind speeds Qingyuan fields at sta- were Xinken and almost Guangzhou consistent stations with were larger than wind fields and the verticalanalysed circulation in by WRF the model following. during the subsidence days were gion at 20:00 LSTdi on 12 Julyat and di at 02:00 LSTthe on Pearl 13 River Estuary, July.by the the They winds sea clearly were breeze. from At show Panyu the that station, south. about 20 km It south was from obviously Central influenced Guangzhou, the As stated in Sect.were moderately 3.2.1, consistent with the the temperature,days measurements and wind during sunny the days. fields subsidence Among simulatedthe days, these rainy most by three important kinds the of to WRF weather, the the model di subsidence days were 3.2.4 Horizontal wind fields from 12 July to 14 July 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ected ff ects, urban ff erences are in- ff erent from those ff usion of air pollutants and ff erent stations are various. These ff ects. When the system background ff 4824 4823 erences between various sites are not apparent. ff erent sites in PRD were analysed by measurements ff ects in PRD areas, such as sea-land breeze e ff N), the flow from the south encounters the mountains and uplifts, ects and mountain valley e ◦ ff ecting the wind fields in Qianyuan. The north of Qianyuan is Nanling ff erent stations was almost ignored. ff nighttime, the ABL turnsseveral to hundred stable metres. and At Xinken thethan station, ABL the those height ABL in decrease height is verydramatically other comparatively from much, lower stations, the just observations. the wind directionCompared and with wind other speed dayshigher also during in 12–15 changed July July. 2006, Thethe stable the weak and horizontal temperature low wind ABL and areresult layer, API the also in descend not the values motion benefit high were and to air the concentrations. di The detailed analyses of wind regimes and thermo-dynamical structure of the wind speed is moderate, theThe di wind fields tend to be similar. The ABL characteristics areABL important features to are identifycalms, the very which air are complex always pollution accompanied in by problem. high PRD pollutant The concentrations. region, However, especially in weak winds and The features of ABLand under sunny three days kinds in ofby weather: July, the 2006 subsidence WRF were days, model. analysedorological rainy with days fields The observations well. results and showin The simulations subsidence that evolution days of the and ABL model sunnydays in can was days. not rainy reproduce The apparent. days diurnal the is variation mete- di of ABLThe evolution height of in the ABL rainy heightstations at Guangzhou, are Panyu, back similar. garden andABL Qingyuan The is diurnal convective variation and process the is maximum obvious. ABL height In can daytime, reach the 1500 m or so. In lower troposphere in PRD showferent that sites there under has small obviousduced background discrepancy by between wind the dif- circumstance. localheat e The island di e – – – – – When the system wind is moderate, the wind fields in PRD regions tend to be similar. also be interpreted byare the summarized detailed as ABL follows. features. The main conclusions by this study results show that thelocal scale characteristics meteorological of conditions ABL couldlution at not meteorological model. be di captured Fine-scale by (atresults a 50 km demonstrated resolution and a of 10 1 successful km km)the simulation meteorological reso- available (WRF) in observations. ABL The main andbe meteorological reasonable used results agreement provided for with by other this studiesresults study in can can PRD be July further intensivesimulation. campaign. The used temporal to The variation meteorological tendency the of model air various air quality pollutant model concentrations can to perform the air concentration 4 Conclusions The characteristics of ABLand at model di results fromcially mesoscale focusing model on WRF during a three comparatively kinds high of API weather, episode espe- during 12–15 July 2006. The urban heat island and mountainthe characteristics valley of in ABL PRD in regions. PRD These unique. local circulationsAt make 03:00 LST on 14 Julyand (Fig. 11b), decreased, the PRD tropical cyclone region “Bilis”PRD was has region already located was made in controlled landfall the bybetween the southwest di north of wind the in cyclone. the low The troposphere. whole The discrepancy circulation a Mountain (about 25 then veers to theby the north mountain-valley at wind high fromsystem the latitude wind slopes and is of descends. the weak, high there Qingyuan mountains. were is Overall, when three always the kinds a of local circulations: sea-land breeze, with the ascend motion in the high vertical latitude. It seems that there was another 5 5 15 10 25 20 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ¨ uggemann, E., Hu, M., ¨ uggemann, E., Herrmann, H., er, D., Deng, A. J., and McQueen, J.: ff 4826 4825 erent wind fields at various sites. Finally, it can ff ect of sea-land breezes on atmospheric haze over the Pearl ff ¨ oschl, U.: Aerosol optical properties in a rural environment near the ect of aerosol water content on visibility impairment and radiative forcing ff This study was supported by funds from China National Basic Research concentrations during an aerosol episode over the Pearl River Delta region of China: 10 the episode in thispanied paper with was subsidence characterised by byculations tropical extremely were complex cyclone responsible ABL, “Bilis”. for accom- di be Thus, summarized simultaneous local that cir- theformation local of the meteorological stable conditions ABL and were the favourable air for pollution the episode. Yang area, Journal of Tropical Oceanography, 3, 21–29, 1985 (in Chinese). 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W.: Mesoscale Structure of Trade Wind Convection over 5 5 30 25 20 15 10 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | T 1.26 − ), wind speed T 4.57 0.35 WD WS − T WD WS 4829 4830 T 1.08 18.33 4.39 0.70 − I II III WD WS 0.46 0.42 0.72 0.45 0.39 0.49 0.61 0.43 0.93 The statistic parametres between the measured 2-m air temperature ( Mean observableMean 254.0 simulationR 2.97 257.9MB 30.86 3.88 29.78 169.3 3.06 187.6 27.29 7.45 27.99 176.6 3.92 1.83 172.0 0.91 30.09 2.18 28.73 MAGERMSEFAE (%) 36.34 1.78 51.07 4.1 2.19 1.80 2.19 14.0 39.02 1.5 4.47 47.39 4.96 1.29 1.53 6.0 52.88 21.9 69.92 0.99 1.22 1.2 1.31 1.63 8.7 14.7 1.2 and Fan S. J.:(PRIDE-PRD2004): Regional overview, Atmos. integrated Environ., experiments 42, on 6157–6173, 2008b. air quality overHazards, 47, Pearl 577–591, River 2008. Delta 2004 for the evaluation of air quality models, Atmos. Sci. 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J., Wiedensohlerg, A., Liu, S.Zhu, C., P.: Andreae, A multiple M. scale O., modelling Wang, system W., for coastal hurricane wind damage mitigation, Nat. Zhang, Y. H., Su, H., Zhong, L. J., Cheng, Y. F., Zeng, L. M., Wang, X. S., Xiang, Y. R., Yu, S., Eder, B., Dennis, R., Chu, S. H., and Schwariz, S.: On the development of new metrics Yu, H., Wu, C., Wu, D., and Yu, J. Z.: Size distributions of elemental carbon and its contribution 5 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4832 4831 Map of PRD area. The sites of measurements are showed. Map of the Guangdong province and its surroundings. Fig. 1b. Fig. 1a. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

:2023 July July) to Ш air pollution air index (API) at Guangzhou station

:14 July to 18 July; 18 Π 4834 4833 :12 Julyto 15 July; Ι during July, 2006 ( 2006 July, during The measured temperature, precipitation and temperature, measured The Fig. 2. Fig. The measured temperature, precipitation and air pollution index (API) at Guangzhou The surface weather situation during 12–15 July 2006.

Fig. 3. Fig. 2. station during July 2006 (I: 12 July to 15 July; II: 14 July to 18 July; III: 20 July to 23 July). 728 729 730 731 732 733 734 735 736 737 725 726 727 715 716 717 718 719 720 721 722 723 724 712 713 714 709 710 711 707 708 702 703 704 705 706 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4836 4835 The observed and simulated 2-m temperature, wind speed and wind direction at Domain settings in WRF model. Fig. 5. Guangzhou from 12 July to 15 July. Fig. 4. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

22 4838 4837 at YuenLong station inHongkong : ppb). x The variation of the modeled WRF planetary boundary layer height (m) for Qingyuan, Back Back Qingyuan, for (m) height layer boundary planetary WRF modeled the of variation The : ppb, NO 2 Fig. 6. 6. Fig.

garden, Guangzhou, Panyu and Xinken stations, and the Lidar normalized relative backscattering signal signal backscattering relative normalized Lidar the and stations, Xinken and Panyu Guangzhou, garden, , SO 3 801 802 795 796 797 798 799 800 793 794 : mg/m 5 . 2 The measured air pollutant concentrations at Guangzhou station from 13 July to 22 July The variation of the modelled WRF atmospheric boundary layer height (m) for Qingyuan, Fig. 7. (unit: PM Back garden, Guangzhou,backscattering signal Panyu at YuenLong and station in Xinken Hongkong. stations, and the Lidar normalized relative Fig. 6. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | : (d)

: observations on 21 July, (c) b d

24 4840 4839 : simulations on 14 July, (b) a c . The vertical wind profile by radio sounding at Panyu station on 14 July and 21 July (a: (a: July 21 and July 14 on station Panyu at sounding radio by profile wind vertical The . Fig. 8 The vertical wind profile by radio sounding at Panyu station on 14 July and 21 July observations in 14b: July, simulations 14 in July, c: observations21 in July, d: simulationsinJuly) 21

The measured vertical temperature profile by radar sounding and the modelled results : observations on 14 July, (a) 855 856 857 858 859 860 861 862 863 864 852 853 854 849 850 851 848 847 842 842 843 844 845 846 at Qingyuan station on 14 July and 21 July. Fig. 9. simulations on 21 July). ( Fig. 8. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | E at 03:00 LST ◦ : 20:00 LST on 12 July, (a) ) along 113.2 1 − : 14:00 LST on 14 July). (d) (a) (b) 4842 4841 . (b) : 08:00 LST on 14 July, (c) (d) (a) (b) (c) and 03:00 LST on 14 July (a) The measured (red arrows) 10-m wind (ms-1) from main meteorological stations in Vertical cross-sections of the WRF modelled wind (m s : 02:00 LST on 13 July, Fig. 11. Fig. 1b and modelled WRF wind field (black arrows) in PRD region ( on 13 July Fig. 10. (b)